1. Field of the Invention
The present invention is directed in general to conveyor systems or any distributed plant, and in particular to monitoring and safety devices associated with such systems.
2. Discussion of the Background
Conveyor lockout and monitoring systems are generally employed in mining and manufacturing operations for overland and underground conveyor belts.
In the operation of any conveyor installation, there is a need for a method of stopping the conveyor in an emergency situation and safely remote isolating the conveyor for maintenance purposes. Several methods exist today to accomplish the basic emergency stop and isolation functions but these have no location information. Existing systems include:                Simple series connection of mushroom or lanyard operated emergency stop switches to the conveyor motor control circuit. This type of system is subject to critical safety issues when simple electrical cable faults exist.        Series connection of mushroom or lanyard operated stop switches with an end of line device to improve safety issues in the presence of simple electrical cable faults.        
These conventional systems suffer from the problems of not providing the name or number, and therefore the location, of the activated switch. Modern conveyors are typically exceeding 4,000 meters in underground installations and 10,000 meters in overland installations so the lack of information as to the location of the activated emergency stop switch or remote isolation switch can be costly in both lost time and loss of life.
Conventionally, conveyors have power available only at the drive points, typically at the head or tail ends of the conveyor. Power is not generally available along the entire length of the conveyor, particularly long overland conveyors through often difficult remote terrain. This lack of power makes location information providing monitoring systems even more difficult which is why most installations are limited to the simple series circuit system described above.
General conveyor operational parameters are also required to be monitored along the entire length of the installation, these include: belt wander, belt tear, belt slip and bearing temperatures, to name a few. These are often difficult to monitor given the distances involved and the lack of power.
Conveyor installations are by their nature hostile environments for any electrical equipment and cabling that may be installed on their superstructure. The equipment and particularly the cabling is subject to vibration, dust, falling material, rain, extremes in temperature and exposure to radiation all of which can result in the introduction of electrical faults that can compromise the integrity and safety of the conventional series connection monitoring systems described above.
Several U.S. patents and published U.S. patent applications in the field of conveyor monitoring describe such applications, and are discussed below as examples of conventional implementations.
U.S. Pat. No. 7,062,355 discloses a method of communicating information among components of a conveyor system where electrical communications architecture includes a central control device, multiple conveyor modules, and an address-based network. In particular, this patent is directed to communication architecture for conveyor systems modularly constructed of connected sections, each section having motorized roller assemblies and associated object sensors sensing objects on the section. The communication signals are provided based upon addresses embedded within the communication signals, the addresses being indicative of at least one of the central control device, the operational devices, the modules and zones associated with the conveyor modules. An address-based network is provided for coupling the central control device with each of the plurality of intermediate controllers, and for sending a plurality of commands from the central control device to the intermediate controllers by way of the address-based network.
U.S. Patent Applications Publication Nos. 2004/0186615 and 2005/0192704 disclose a control system with an additional feature of a logic system 84 that may be adapted to execute stored programs according to certain parameters and messages received from a master device to, for example, provide start/stop and speed control to the motorized rollers of conveyor sections. Each of these published applications is directed to specific implementations of such a logic system to facilitate a more flexible control of conveyor systems constructed of multiple independently-powered conveyor modules as described in the patent application that issued as U.S. Pat. No. 7,062,355.
U.S. Patent Application Publication No. 2008/0097624 discloses a system applicable to state processing in an industrial control environment that implements a system having module components to facilitate the processing. In particular, this published application discloses a system where propagation components are embedded within the module components to communicate state information to at least one other module component of the system. The communicated state information includes control information relating to reset, mode and faults, and the state propagation components are provided within a hierarchical architecture where the control information is communicated up or down the hierarchy of modules. Components associated with system 100 illustrated in this published patent application can include various components that propagate safety data up and down the hierarchy including presence sensing devices, safety switches, interlock switches, safety relays, emergency stop devices, cable pulls and enabling switches, safety controllers, and so forth which are capable of interacting to form a safety system. Safety Integrity Level (SIL) is noted as one of the functional safety aspects provided by a system implementing the propagation components that propagate the safety data.
U.S. Pat. No. 5,186,308 discloses a control system for industrial conveyor systems which include plural individual conveyor. In particular, an electrical control system for such a conveyor system comprises a main controller which is located at any selected location in a factory and sub-controllers each mounted on or located immediately adjacent the respective conveyors sections. The conveyor system includes at least two individual conveyors that interact with each other and must be operated in a timed relationship. Information from/to sub-controllers is transmitted via a dedicated communication line to the main controller in which signals are processed by a PC operating under the control of a diagnostic program.
U.S. Pat. No. 6,705,454 discloses a controller for an accumulating power roll conveyor system having a series of modular sections divided into multiple independently powered zones each zone having an actuator for driving the rollers of the zone and a part sensing member for detecting the presence of a part in the zone. The controller implements an analog (specifically, not digital) electrical circuit to facilitate precise physical stoppage for parts moving in each zone by controlling the part sensing members and the actuators.
U.S. Pat. No. 7,269,465 discloses a control system for controlling safety-critical processes that includes a field bus, a bus master for controlling communication via the field bus, a signal unit connected to the bus master via the field bus for linking to a safety-critical process and a control unit for controlling the safety-critical process. The background section of the specification generally describes a control and data transmission installation in which safety-related devices can communicate with one another via a field bus, and the safe control is affected using the field bus. An added feature disclosed in the U.S. Pat. No. 7,269,465 patent is implementation of a bus master to more effectively control communication with a plurality of signal units via the field bus.
U.S. Patent Application Publication No. 2008/0097624 relates to process devices used to monitor operation of an industrial process, and discloses an apparatus for use in a process device to provide a desired Safely Integrity Level (SIL) for the process device. According to this published patent application, process devices include control devices, such as conveyors, and process monitors which monitor operation of the process. In particular, a supervisory overlayer for use with or in a process device is disclosed. The supervisory overlayer monitors operation of the process device and is used to prevent, mitigate and/or detect failure of component(s) or other aspects of the device, including the supervisory overlayer itself.
None of the above-described patents or patent applications discloses a conveyor monitoring system where pulse width modulation and amplitude modulation are used for communication between field devices (such as remote isolation switches deployed at various locations of a conveyor belt) and a central controller, and for indication of the device location. Furthermore, none of these patents or patent applications discloses a fail safe redundant switching system for a conveyor control circuit where additional transmitter and receiver modules are provided in combination with the means for accurate indication of switch location to achieve SIL 3 rating.
The ability to provide control (analogue and digital outputs) along the length of the conveyor is also an advantage, particularly when the control outputs are line powered, that is provided by a field bus system that provides both power and signaling on the same network.
An example of a system available from Austdac Pty. Ltd. is illustrated in a block diagram of FIG. 1A and corresponding schematic of FIG. 1B where a conveyor control panel 100 connects to emergency stop switches 102, which can be impended as pullkeys, via a field bus 104. As shown in FIGS. 1A and 1B, the system includes selector switches 108 wired to operate a remote isolation function, and a tail end unit 106 that has end of line transmitters P1 and P2.
Other examples of systems available from Austdac Pty. Ltd. are described in published Austdac Pty. Ltd. documents numbers 03-126-35-xx06-15, 03-168-35-xx04-12, 03-210-35-xx02-12, 03-240-35-xx01-06 and 04-001-43-xx23-01, available for review at www.austdac.com.au. The entire contents of these published Austdac Pty. Ltd. documents are incorporated herein by reference. One of ordinary skill in the art would readily appreciate how systems such as those described in these published Austdac Pty. Ltd. documents can be configured to incorporate certain exemplary features of the embodiments of the present invention based on the teaching and disclosure set forth below in the DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION.
By introducing a device at each emergency stop or lanyard switch that can indicate to the conveyor monitoring system that an emergency stop or lanyard switch has been activated and also provide an unique code to indicate which switch has been activated can therefore provide the location of the switch along the conveyor is able to solve many of the issues involved with conventional conveyor installations.
Location information also increases the integrity and therefore the safety of the system by allowing diagnostics to be carried out using location information to determine if cable open circuit faults or faults involving earth or conveyor structure have occurred. This information can be used to provide warnings or automatically shut down the conveyor.